Apparatus for displacing scum in continuous casting molds



R. J. KEENE Aug. 6, 1968 APPARATUS FOR D ISPLACING SCUM TN CONTINUOUS CASTING MOLDS 2 Sheets-Sheet 1 Filed Sept. 1, 1965 mm. M

INVENTOR J-KEENE ROBERT ym/422% ATTORNEY Aug. 6, 1968 R. J. KEENE APPARATUS FOR DISPLACING SCUM IN CONTINUOUS CASTING MOLDS Filed Sept. 1, 1965 2 Sheets-Sheet f1:

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INVENTOR ROBERT J K E ENE BY fl ATTORNEY United States Patent M 3,395,750 APPARATUS FOR DISPLACING SCUM IN CONTINUOUS CASTING MOLDS Robert J. Keene, Chicago Heights, 11]., assignor to United States Steel Corporation, a corporation of Delaware Filed Sept. 1, 1965, Ser. No. 484,407 1 Claim. (Cl. 164259) ABSTRACT OF THE DISCLOSURE Transverse manifolds are disposed above a rectangularsection continuous-casting mold, adjacent the median transverse plane, and are provided with nozzles extending down into the mold cavity directed to discharge gas jets sweeping the surface of the molten metal and causing floating slag to accumulate adjacent the end walls. A guide plate having target marks for the jets is temporarily inserted in the mold before pouring to facilitate directional adjustment of the nozzles.

This invention relates to methods and apparatus for continuous casting of steel, and more particularly to methods and apparatus for displacing scum from the molten metal surface in a continuous casting mold in such manner that subsequent surface conditioning of a casting formed in said mold may be minimized.

In the continuous casting of metals and particularly steel, liquid steel is poured from a ladle, either directly or through an intermediate vessel such as a tundish, into the upper end of an open-ended water-cooled tubular casting mold. Solidification of the casting is initiated in the mold. A partially solidified casting having a thin solidified shell surrounding a liquid core or metal is continuously discharged from the mold. As this casting descends, it is cooled with water causing gradual complete solidification of the casting.

Continuously formed castings of large cross-sectional area are generally in the shape of rectangular slabs. Rectangular slabs can be cooled, solidified, and rolled more readily than castings of other shapes having comparable cross-sectional areas.

The molten metal teemed into the mold contains small amounts of impurities, chiefly oxides of iron and other metals and metalloids in the steel. Examples of these oxides are iron oxide, manganese oxide, alumina and silica. They are lighter than steel, and float on the surface of the liquid metal in the mold. They tend to agglomerate into large islands of scum or slag on the molten steel surface.

The oxide impurities are drawn toward the mold walls, and descend along the surfaces of the casting as the casting descends. As the casting is solidified, the oxide impurities freeze on the surfaces of the casting. Generally these oxide impurities cover substantial portions of both the broad faces and the edges of the casting, which are formed along the side walls and the end walls respectively of the mold. These impurities must be removed from the casting surface by suitable procedure such as scarfing. The oxide impurities on the casting surface also impede heat transfer from the casting because of their low thermal conductivity. solidification of steel is retarded. As a result, the casting shell in the vicinity of the oxide impurities may be so thin that it cannot withstand the lateral pressure of the molten metal in the casting core as the partially solidified casting descends below the mold. Breakouts may result from this condition.

An object of this invention is to provide a method and apparatus for directing oxide impurities toward at least one predetermined portion of the walls of a continuous casting mold, so that they will be concentrated along this portion of the walls, leaving the remainder of the walls 3,395,750 Patented Aug. 6, 1968 substantially clean, and thereby minimizing the detrimental effect on heat transfer and the amount of casting surface which must be conditioned in order to remove the oxide impurities. More particularly, an object of this invention is to provide a method and apparatus for directing oxide impurities toward the end walls in a mold of rectangular cross section, so that they will be concentrated along the end walls, leaving the side walls substantially clean.

This invention provides a pair of gas manifolds and a plurality of jets extending therefrom, directed against the molten metal surface in a continuous casting mold of rectangular cross section in such manner that the force of the gas streams issuing from the jets blows the oxide impurities toward the end walls of the mold. This concentrates the impurities along the edges of the casting, so that the broad faces of the casting which are formed along the side Walls of the mold are substantially clean and free from non-metallic surface deposits. These oxide impurities can be removed from the casting after it solidifies by conditioning the edges thereof.

In the drawings:

FIG. 1 is a front elevational view, shown partly in section, of my invention, showing a bottom pour ladle, an open-ended tubular continuous casting mold in fragmentary representation, and the gas manifolds and gas jets.

FIG. 2 is a top plan view of the apparatus looking downwardly along line 2-2 of FIG. *1.

FIG. 3 is a top plan view of a mold and rectangular plate used for aligning the jets prior to casting.

FIG. 4 is a vertical sectional view taken along line 44 of FIG. 3.

Referring now to FIGS. 1 and 2 of the drawing, 10 is a bottom-pour ladle containing molten steel and having a discharge nozzle 11. This ladle is positioned directly over an open-ended tubular water-cooled flow-through continuous-casting mold 12. Mold 12 is of rectangular cross section having a pair of opposed parallel side walls 13 and a pair of opposed parallel end walls 14. A plate 15 is provided on top of mold 12. Cooling water circulates through the side and end walls 13 and 14 respectively in passages not shown.

A pair of gas manifolds 16 having a plurality of nozzles 17 extending therefrom supply an inert compressed gas such as argon or nitrogen, which blows the non-metallic impurities on the surface of molten metal in mold 12 away from the nozzles 17 and toward the end walls 14 of the mold. Manifolds 16 extend laterally across mold 12, substantially parallel to end walls 14. Manifolds 16 may rest on plate 15, or may be supported in elevated positions thereabove. These manifolds have clamps 18 welded thereto, and these clamps 18 in turn are tack welded to plate 15. Manifolds 16 are parallel and are spaced far enough apart so as not to inte-refere with the molten steel stream teemed from nozzle 11 into mold 12. Manifolds 16 are also at a substantial distance from end walls 14, so that they will effectively sweep most of the surface of molten metal in mold 12. Nozzles 17 are preferably thin tubes of copper or other suitable metal, extending vertically below manifolds 16 bent at their ends so as to direct the compressed gas flowing therethrough downwardly against the molten metal of surface in the mold and outwardly toward the end walls 14 of the mold. T fittings 19 provide joints between manifolds 16 and nozzles 17.

The tips of nozzles 17 direct the gas streams issuing therefrom in directions substantially parallel to side walls 13. The nozzles of each manifold 16 are directed downwardly against the molten metal surface and away from the other manifold, so that the gas issuing from the jets will blow the oxide impurities on the surface of the metal toward the end walls 14. As a result, the non-metallic impurities are concentrated along the edges of the solidified casting, and the faces of the casting are almost entirely free of metal oxides. The tips of nozzles 17 are not necessarily all directed downwardly at the same angle. In fact, it is desirable for the nozzles to be directed at slightly different angles, so that the gas jets issuing from these nozzles will strike the molten metal surface at different distances from the lateral center line of the mold. This improves the efiiciency of conveying metal oxides toward the end walls 14.

As a specific illustration of the apparatus of this invention, the continuous-casting mold 12 has a mold cavity of rectangular cross section measuring 7.5 by 27 inches. A pair of inert gas manifolds 16, each having an inside diameter of /2 inch, are used. Five nozzles 17 extend from each manifold, consisting of A inch copper tubing. The tips of nozzles 17 are 3 to 5 inches above the liquid level in the mold and about 7 to 8 inches from the interior end walls 14. The mold is filled with liquid steel to a depth of 410.5 inches below the top of the mold after the manifolds 16 and nozzles 17 have been put in place. This depth is maintained throughout casting. An inert gas, either nitrogen or argon, is supplied under a slight positive pressure throughout the entire casting operation. The gas-flow rate through each jet is about 2 to 5 standard cubic feet per minute.

The nozzles 17 may be properly adjusted prior to the start of a casting by using a rectangular gage plate 20 shown in FIGS. 3 and 4. Plate 20 has a plurality of spot marks 21, herein shown as cross marks arranged in two rows. These spot marks 21 indicate the locations toward which nozzles 17 are directed. One spot mark is provided for each nozzle 17. The positions of spot marks 21 are preferably staggered since this makes for more efficient removal of scum from the molten metal surface toward end walls 14. Plate 20 is supported in the cavity of mold 12 at the same depth as the mean liquid level during casting. To support plate 20 at the desired depth, a pair of laterally extending U-shaped handles 22 near the mold end walls 14 have arms 23 which engage plate along the side walls 13 of the mold. Handles 22 are secured to brackets 24 integral with plate adjacent the four corners thereof by means of pins 25. The vertical arms of handles 22 have screw-threaded portions 26 which receive internally screw-threaded sleeves in arms 23, permitting adjustment of the depth of plate 20 in the mold cavity.

After plate 20 has been placed in position, manifolds 16 and nozzles 17 are put in place, the nozzles having been fabricated and bent in advance so as to direct their gas streams toward the approximate locations desired. All jets issuing from nozzles 17 are directed longitudinally, parallel to mold side walls 13. Plate 20 provides a convenient means for determining if there has been any error in the aiming of the' nozzles 17.

After the nozzles have been adjusted, plate 20 is removed. This is accomplished by pulling out the pins 25 at one end of plate 20, allowing that end of the plate to drop in a rotary path about the pins 25 at the opposite ends as pivots. Plate 20 is then pulled out of the mold cavity by the handle 22 to which it remains attached, After removal of plate 20, manifolds 16 are tack welded in place. The apparatus is then ready for casting operations.

Although this invention hasbeen described with particular reference to a mold of'rectangular'cross section for purposes of illustration, the mold may be of other cross-sectional shapes if desired. The nozzles 17 are arranged so that the scum is directed toward at,least one predetermined portion of the mold wall. The scum descends with the casting along this portion of the mold wall, and the remainder of the casting surface is relatively free of impurities.

The present invention provides a simple method and apparatus for disposing of non-metallic impurities floating on the surface of the mold, so that they impair only a minimum portion of the casting surface. This apparatus makes it possible to dispense with operators standing over the mold 12 during teeming operations and manually removing floating impurities onthe surface of the molten metal in mold 12.

While this inventioin has been explained with reference to a specific embodiment thereof, it is understood that modifiications can be made by those skilled in the art without departing from the scope and spirit of this invention.

What is claimed is:

1. The combination with a rectangular-section tubular mold having side and end walls defining a cavity, disposed with its longitudinal axis substantially vertical, of a manifold extending across the top of the mold cavity bridging the side walls and being connected to a supply of inert gas and nozzles extending downwardly from said manifold, the ends of the nozzles being inclined laterally toward one of said end walls.

References Cited 7 UNITED STATES PATENTS 2,876,509 3/1959 Gardner 16428l 2,962,277 11/1960 Morrill l64283 X 3,089,209 5/1963 Phillips et al. l64-66 2,023,957 12/1935 Hewgill 164-134 XR 3,300,824 1/1967 Ross 16466 FOREIGN PATENTS 656,386 8/1951 Great Britain.

J. SPENCER OVERHOLSER, Primary Examiner.

R. S. ANNEAR, Assistant Examiner. i 

